1. Field of the Invention
The present invention relates to a gear mechanism for allowing a pair of driven gears to be rotated in an arbitrary direction by a single driving gear rotating clockwise or counterclockwise.
More particularly, the present invention relates to a gear mechanism in which one of the pair of the driven gears, for example, a right-side driven gear, is always rotated counterclockwise and a left-side driven gear is always rotated reversely by the single driving gear rotating clockwise or reversely.
2. Description of the Related Art
In a known gear mechanism having first and second intermediate or drive transmission gears ("intermediate gears") and left-side and right-side driven gears the intermediate gears are rotatably mounted on opposite ends of a lever which is rotatable on its central part as a rotating shaft.
The first intermediate gear is engaged with a single driving gear as well as with the second intermediate gear.
Clockwise rotation of the driving gear causes the lever to be rotated due to a turning force thereof. Consequently, the first intermediate gear is engaged with the left-side driven gear to cause the latter to be rotated clockwise.
By contrast, the second intermediate gear is engaged with the right-side driven gear to cause the latter to be rotated counterclockwise.
Then, counterclockwise rotation of the driving gear causes the lever to be reversely rotated due to the turning force thereof. Consequently, the first intermediate gear is engaged with the right-side driven gear to cause the latter to be rotated counterclockwise. By contrast, the second intermediate gear is engaged with the left-side intermediate gear to cause the latter to be rotated clockwise.
In order to rotate the lever by forward/backward rotation of the driving gear, it is necessary to apply a slight tension to the second intermediate gear employing a bias spring.
Namely, the bias spring is arranged to apply tension to the tooth face of the second intermediate gear in the direction of the first intermediate gear.
As described above, the turning force of the driving gear produced due to clockwise/anticlockwise rotation thereof causes the left-side driven gear to be always rotated clockwise as well as the right-side driven gear to be always rotated counterclockwise.
Such a prior gear mechanism suffers from the following difficulties:
(1) Backlash between the driving gear and the first intermediate gear is increased following the rotation of the lever and becomes a maximum when main power is transmitted, or the first intermediate gear is engaged with the right-side or left-side driven gear.
(2) Since both of the intermediate gears are moved integrally with the lever, so that if the dimensional accuracy of the system is not ideal, engagement of either one of the intermediate gears with the driven gear causes the rotation of the lever to be stopped, resulting in backlash between the other intermediate gear and the driven gear.
(3) Integral movement of the intermediate gears with the lever causes turning force to be transmitted simultaneously to the driven gears. Accordingly, any load applied to the driven gears is rapidly increased.
(4) In addition, the intermediate gears are integrally mounted in the lever, so that no intermittent operation is made possible wherein a turning force of the driving gear is transmitted only to one of the driven gears.